Electroplating apparatus



June 7, 1960 J. K. HAUSNER ELECTROPLATING APPARATUS Original Filed Aug. 3. 1955 I 2/ DIRECT CURRENT 4 SOURCE Unite-x1 states t nt 2,939,828 ELECTROPLATIN G APPARATUS Johann KarlHansner, Chicago, 111., asslgnor to Karl K.

- Kaempfer, Harrington, lll.

Qriginalapplication Aug. 3, 1955, Ser. No.

2 Claims. or. 204-228) This invention .relates to electroplating apparatus and more particularly to electroplating apparatus in which high frequency alternating current fields are superimposed on a direct current field in a plating bath.

This application is a division of my copending application entitled Electroplating, filed August 3, 1955, Serial No. 526,193, now Patent No. 2,824,830, which, in turn, is a continuation-in-part of my copending applica tion Serial No. 327,402, entitled Method for High Frequency Galvanic Separation of Metals and Products Obrained Thereby," filed December '22, 1952, now aban- .doned.

As discussed in said applications, the electroplating of a metal onto a given article involves immersing the article to .be plated in an electrolyte and passing an electric current through the electrolyte between the article and another electrode also irnmerscd in the electrolyte' The electrolyte contains a metal tobe plated and additional plating metal may be added to the electrolyte either by adding additional quantities of a salt of the metal to the electrolyte or, in certain cases, by employing an electrode made of metal which will supply metal to the electrolyte solution when subjected to the direct current employed in the plating process. l

As further discussed in said applications, it is highly advantageous to superimpose on the direct ,"current field an alternating current field, to greatly improve the plating action. It has, also been found highly advantageous to use a plurality of alternating current fields. of differ ing frequencies.

Aprimary object of this invention is to provide an improved apparatus for generating and applying alternating current fields to an electroplating bath.

1 According to this invention, the article to be plated p andthe plating electrode are immersed in an electrolyte and the article and the electrode are connected to'a suitabledirect current source. The article and the electrode are also coupled to. a high frequency source. According to a specific featurejof the invention the high frequency source is connected in' parallel relation to the direct current source, and most preferably through at least one series capacitor.

A further important feature of the invention is in the generation of two high frequency currents of differing frequencies. According to this feature, a single oscillator is used to simultaneously apply two different frequencies to thus eliminate the need for two separate oscillators. This highly advantageous result is achieved by using a relatively high degree of coupling between an h sc'illator tank coil and a coil coupled to the plating bath.

This invention contemplates other and more specific objects, features and advantages which will become more fully apparent from the following detailed description taken in conjunction with the accompanying drawing, in which the single figure is a diagrammatic view including a wiring diagram and a plating tank connected thereto.

Reference numeral .10 designates an electrode which is immersed in an electrolyte and a tank 11, with an article 12 to be plated being also immersed in the plating bath. As an example, the plating maybe carried outin a chrome plating bath with the electrode 10 being in the form of a lead anode and with the article 12 being of brass toconstitute a cathode. As another example, the electrolyte may contain zinc, with the electrode 10 being a zinc anode and with the electrode 12 being a brass cathode. As another example, the plating may be carried out in an electrolyte containing copper with the electrode 10 being of copper and with the article12 being of brass. Specific examples of the plating opera, tion are described in detail in my prior patent applications mentioned heretofore.

To effect the plating operation, a direct current field is applied to the plating bath, and high frequency fields are superimposed on the direct current field. The best results are obtained by using at least two high frequency fields those frequencies, expressed in wave lengths in air, are of a magnitude of 1.8 to 16 meters and which differ from one another by a magnitude of 2 to 40% of their average wave length. Preferably, the frequencies are of a magnitude of 3.5 to 6.5 meters and differ from one another by magnitude of 5 to 20% of their average wave length. However, it is possible to use frequencies outside these ranges.

To apply the DC. field to the plating path, the anode 10 is connected through a conductor 17 and an ammeter 18 to one terminal 19 of a direct current source 20 having a second terminal 21. connected through a conductor 22 to the cathode 12. The source 20 may be any source of steady or pulsating current. Batteries may be used or where standard 25, 50 or 60 cycle alternating current is available, it will ordinarily be preferably to provide rectifiers to convert the alternating current to direct current.

To apply a high frequency field to the plating bath, certain points of the conductors 17 and 22 are respectively connected throughcoupling capacitors 23 and 24 to the terminals of a coil 25 which may have a variable tuning capacitor 26 connected in parallel therewith. The coil 25 is inductively coupled to a tank coil 27 of an oscillator generally designated by reference numeral 28, which comprises a triode vacuum tube 29 having a plate or anode 30, a control grid 31 and a directly heated cathode or filament 32. The oscillator may be a seriesfed Hartley type with the plate 30 being connected to one end of the tank coil 27, with the grid 31 being con- "'nected to the other end of the tank coil 27 through a DC. blocking capacitor 33 w and with a plate supply voltage being connected between a tap 34 on the coil 27 and the filament 32. t

A source of direct cur-rent may be used for the plate supply but preferably, to eliminate the need for rectifiers; an alternating currentsupply is used. In particular, the filament 32 is connected to one terminal of a high voltage secondary winding 35 of a transformer 36 and the tap 34 is connected through a choke coil 37 to the other terminal of the winding 35. a

To heat the fialment 32, one side thereof is connected to one side of a secondary winding 38 of a transformer 39, the other side of the filament being connected through an ,ammeter 40 and a rheostat 41 to the other side of the winding 38. The transformers 36 and 39 have pri-, maries 42 and 43 connected in parallel to terminals'44 and 45 which may be connected in parallel toterminals 44 and 45 which may be connected to a suitable AC source, such as a source of 60 cycle, 220 voltcurrent. Grid-leak bias is preferably used for the oscillator- 2$ to insure selfstarting, the grid 31 being connected through the parallel combination of a resistor 46 and a capacitor 47 to the filament 32.

With the coil 23 being tuned by the capacitor 26, it is not necessary to tune the coil 27. However, it may in some circumstances be-dcsirable to connect a variable capacitor 48 across the coil 27.

It will be appreciated that with the oscillator circuit as thus far described,'a high frequency field of one frequency may be readily applied to the plating bath. To apply a high frequency field of a different frequency, a

separate oscillator maybe used. According to an 1mdegree of coupling results in the generationof two fre- 'quenciesbecause of the fact that when two resonant cir cuits are coupled together with acoefficient of coupling greater. than a certain amount,=-two resonant peaks will exist at frequencies respectively above and below the frequency to which the circuits are tuned (which hereinbefore is referred to as the average frequency). The oscillator circuit may thus have the greatest degree of amplification'at two different frequencies and can operate simultaneously at both frequencies.

'If the oscillator output is viewed on an oscilloscope, for example, the wave will have the same general form as is produced by the addition of two sine waves. As is well known, beat frequencies may be produced from waves of two different frequencies and such beat fre- 'quencies are produced by the oscillator of the system of this invention.

It should be noted that the greater the degree of'coupling, the more prominent are the pair of resonant peaks and the greater is the spacing or frequency difierence therebetween. Thus, the relation of the two frequencies can be adjusted by adjusting the coupling between the coils 25 and 27.

In practice, the coupling is generally adjusted until optimum performance is achieved. In any case, the coupling should be such that the mutual inductance in henrys is substantially greater than where R is the resistance of one coil in ohms, R is the resistance of one coilin ohms, R is the resistance of the other coil in ohms and w=21rf, f being the frequency to which tuned, .in cycles per'second. A coupling such that is generally termed critical coupling and hence the coupling should be substantially greater than critical coupling.

By way of illustrative example and not by way of limitation, the capacitors 23 and 24-may each have a capacitance of 2000 micro-microfarads; the capacitor 26 may have a maximum capacitance of 125 micro-microfarads; the capacitor 33 may be constituted by two vacuum capacitors each having a capacitance of 25.0 micro microfarads; the capacitance 47 may have a capacitance of 100 micro-microfarads; the resistor 46 may have a value of 10,000 ohms; the voltage developed across the secondary 35 may be 5000 volts R.M.S.; and the-tube 29 may be an air-cooled high vacuum type with 2000 watts maximum power output. As above indicated,.the capacitor 48 is not necessary.

It is a specific featureof the invention that the high 'frequency source is connected in parallel relation to the direct current source. A series coupling could be used but such would necessitate that the DC. source have a very low internal impedance to the high frequency currents to obtain eflicient operation. This is diflicult to achieve, particularly with the relatively long conductors usually used to connect the DC. source to the electrodes.

With a parallel coupling such as shown, the impedance of the high frequency current path through the plating bath should be much less than the impedance of the path through the DC. source. With conductors of substantial length as are usually used to connect the DC. source to the plating bath, this 'is achieved to a certain extent by merely connecting the high frequency source to points on the conductors 17, 22 close to the anode 10 and cathode 12. If desired, in addition, choke coils-may be provided between the terminals of the D..C. source and the points to which the high frequency source is connected. a

As disclosed and claimed in my copending application Serial No. 526,193, the positions of connection of the high frequency source to the conductors 1.7, 22may be adjusted to obtain optimum coupling to the bath. With frequencies in the'ranges previously specified, theconductors 17, 22 canform a transmission lineof substantial length as compared to one wave length, and by moving the points of connections to the conductors 17, 22, resonant and anti-resonant points (or nodes and anti-nodes) may be found and by using the resonant points, optimum coupling can be achieved. In many cases, points can be found at which the high frequency current path through the bath is resonant with the high frequency path through the direct current source being anti-resonant so that the ideal coupling can be achieved.

It'will be understood that modifications and variations may be effected without departing from the spirit "and scope of the novel concepts of this invention.

I claim as my invention: v

1. In an electroplating system in which an article-to be plated and a plating electrode are immersed in an electrolyte, a direct current source connected to "said article and said plating electrode, an oscillator including a tank coil and an output coil inductively coupled to-said tank coil, means for coupling said output coil to said article and said plating electrode, capacitance means for turning at least one of said coils to a certain resonant frequency, the coupling between said coils being substantially greater than critical-coupling to obtain two output frequencies on either side of said certain resonant frequency.

2. In an electroplating system in which an .articleto be plated and a plating electrode are immersed in an electrolyte, a direct current source connected to said article and said plating electrode, an oscillator including a tank coil and an output coil inductively coupled to said tank coil, means for coupling said output coil to saidarticle'and said plating electrode,. c apacitance means for turning at least one of said coils to a herta'in resonant frequency, the coupling between said coils being sub-f stantially greater than critical coupling 'to obtain two output frequencies on either side of said certain resonant frequency, and at least one capacitor connected in series between said output coil and said 'articleand plating electrode.

References Cited in the file 'of this patent UNITED STATES PATENTS 

1. IN AN ELECTROPLATING SYSTEM IN WHICH AN ARTICLE TO BE PLATED AND A PLANTING ELECTRODE ARE IMMERSED IN AN ELECTROLYTE, A DIRECT CURRENT SOURCE CONNECTED TO SAID ARTICLE AND SAID PLATING ELECTRODE, AN OSCILLATOR INCLUDING A TANK COIL AND AN OUTPUT COIL INDUCTIVELY COUPLED TO SAID TANK COIL, MEANS FOR COUPLING SAID OUTPUT COIL TO SAID ARTICLE AND SAID PLATILNG ELECTRODE, CAPACITANCE MEANS FOR TURNING AT LEAST ONE OF SAID COILS TO A CERTAIN RESONANT FREQUENCY, THE COUPLING BETWEEN SAID COILS BEING SUBSTANTIALLY GREATER THAN CRITICAL COUPL-ING TO OBTAIN TWO OUTPUT FREQUENCIES ON EITHER SIDE OF SAILD CERTAIN RESONANT FREQUENCY. 